1. Field of the Invention
The present invention relates to a vibration-insulating rubber molded product for use in an automobile, etc., particularly to a vibration-insulating rubber molded product having flash, where defects such as damage of a mold used for forming the product can be easily found by visually observing the flash.
2. Description of the Related Art
When parts such as an engine are installed in an automobile body, a vibration-insulating rubber molded product is generally inserted therebetween to insulate the parts from vibration. Since the vibration-insulating rubber molded product for the engine is exposed to a high temperature, the product is required to have excellent heat resistance. Thus, an ethylene-propylene-diene rubber (EPDM), etc. has been widely used therefore.
As a rubber composition for such a vibration-insulating rubber molded product, Japanese Patent Laid-Open, No. 5-239289 has proposed a vulcanizable rubber composition comprising: an ethylene-propylene-nonconjugated diene rubber or a blend of an ethylene-propylene-nonconjugated diene rubber and a diene rubber; a particular alkoxysilane compound; and fine powdery silicic acid and/or a silicate having specific surface area of 5 to 100 m2/g (BET adsorption).
The rubber composition further comprises 0.1 to 60 weight % of a carbon black having specific surface area of 5 to 90 m2/g with excellent dynamic properties, mechanical strength, dynamic fatigue resistance, heat aging characteristics, etc.
However, according to specific examples described in Japanese Patent Laid-Open No. 5-239289, the rubber composition comprises 20 to 40 weight % of the carbon black, and is entirely opaque with black color. A portion having a thickness of approximately 1 mm or less in flash of the molded product produced therefrom is also substantially opaque, therefore, the thickness of the flash cannot be evaluated by visual observation.
In general, the vibration-insulating rubber molded product is produced by a insert molding method to stick it integrally on a frame of a part. The insert molding method comprises the steps of placing the frame of the part in a cavity of a mold, injecting the rubber composition thereinto, and integrally forming them. On the outskirt of thus-obtained rubber molded product, the flash is unavoidably formed along mold-releasing surfaces of the mold. In the case where it is normally formed, in other words, in the case where the mold does not have any damage such as cutout, the thickness of the flash is almost 1 mm or less. In contrast, in the case of a mold with damage, the thickness of the flash corresponding to the damage comes to be thicker. The thicker portion of the flash is apt to be degraded by heating and become cracked, thereby often causing rupture of the entire vibration-insulating rubber molded product.
If the thickness of the flash can be easily evaluated, it becomes possible to prevent the vibration-insulating rubber molded product from cracking, and to find the damage of the mold causing increase of the thickness. However, the conventional vibration-insulating rubber molded product comprises the silica powder without carbon black to be white, or comprises a large amount of carbon black to be black. Consequently, the thickness of each portion of the flash must be measured to find the thicker portion, and it is difficult to easily evaluate whether the flash includes the thicker portion.